Add -ftrivial-auto-var-init option and uninitialized variable attribute.

Initialize automatic variables with either a pattern or with zeroes to increase
the security and predictability of a program by preventing uninitialized memory
disclosure and use.
GCC still considers an automatic variable that doesn't have an explicit
initializer as uninitialized, -Wuninitialized will still report warning messages
on such automatic variables.
With this option, GCC will also initialize any padding of automatic variables
that have structure or union types to zeroes.
You can control this behavior for a specific variable by using the variable
attribute "uninitialized" to control runtime overhead.

gcc/ChangeLog:

2021-09-09  qing zhao  <qing.zhao@oracle.com>

	* builtins.c (expand_builtin_memset): Make external visible.
	* builtins.h (expand_builtin_memset): Declare extern.
	* common.opt (ftrivial-auto-var-init=): New option.
	* doc/extend.texi: Document the uninitialized attribute.
	* doc/invoke.texi: Document -ftrivial-auto-var-init.
	* flag-types.h (enum auto_init_type): New enumerated type
	auto_init_type.
	* gimple-fold.c (clear_padding_type): Add one new parameter.
	(clear_padding_union): Likewise.
	(clear_padding_emit_loop): Likewise.
	(clear_type_padding_in_mask): Likewise.
	(gimple_fold_builtin_clear_padding): Handle this new parameter.
	* gimplify.c (gimple_add_init_for_auto_var): New function.
	(gimple_add_padding_init_for_auto_var): New function.
	(is_var_need_auto_init): New function.
	(gimplify_decl_expr): Add initialization to automatic variables per
	users' requests.
	(gimplify_call_expr): Add one new parameter for call to
	__builtin_clear_padding.
	(gimplify_init_constructor): Add padding initialization in the end.
	* internal-fn.c (INIT_PATTERN_VALUE): New macro.
	(expand_DEFERRED_INIT): New function.
	* internal-fn.def (DEFERRED_INIT): New internal function.
	* tree-cfg.c (verify_gimple_call): Verify calls to .DEFERRED_INIT.
	* tree-sra.c (generate_subtree_deferred_init): New function.
	(scan_function): Avoid setting cannot_scalarize_away_bitmap for
	calls to .DEFERRED_INIT.
	(sra_modify_deferred_init): New function.
	(sra_modify_function_body): Handle calls to DEFERRED_INIT specially.
	* tree-ssa-structalias.c (find_func_aliases_for_call): Likewise.
	* tree-ssa-uninit.c (warn_uninit): Handle calls to DEFERRED_INIT
	specially.
	(check_defs): Likewise.
	(warn_uninitialized_vars): Likewise.
	* tree-ssa.c (ssa_undefined_value_p): Likewise.
	* tree.c (build_common_builtin_nodes): Build tree node for
	BUILT_IN_CLEAR_PADDING when needed.

gcc/c-family/ChangeLog:

2021-09-09  qing zhao  <qing.zhao@oracle.com>

	* c-attribs.c (handle_uninitialized_attribute): New function.
	(c_common_attribute_table): Add "uninitialized" attribute.

gcc/testsuite/ChangeLog:

2021-09-09  qing zhao  <qing.zhao@oracle.com>

	* c-c++-common/auto-init-1.c: New test.
	* c-c++-common/auto-init-10.c: New test.
	* c-c++-common/auto-init-11.c: New test.
	* c-c++-common/auto-init-12.c: New test.
	* c-c++-common/auto-init-13.c: New test.
	* c-c++-common/auto-init-14.c: New test.
	* c-c++-common/auto-init-15.c: New test.
	* c-c++-common/auto-init-16.c: New test.
	* c-c++-common/auto-init-2.c: New test.
	* c-c++-common/auto-init-3.c: New test.
	* c-c++-common/auto-init-4.c: New test.
	* c-c++-common/auto-init-5.c: New test.
	* c-c++-common/auto-init-6.c: New test.
	* c-c++-common/auto-init-7.c: New test.
	* c-c++-common/auto-init-8.c: New test.
	* c-c++-common/auto-init-9.c: New test.
	* c-c++-common/auto-init-esra.c: New test.
	* c-c++-common/auto-init-padding-1.c: New test.
	* c-c++-common/auto-init-padding-2.c: New test.
	* c-c++-common/auto-init-padding-3.c: New test.
	* g++.dg/auto-init-uninit-pred-1_a.C: New test.
	* g++.dg/auto-init-uninit-pred-2_a.C: New test.
	* g++.dg/auto-init-uninit-pred-3_a.C: New test.
	* g++.dg/auto-init-uninit-pred-4.C: New test.
	* gcc.dg/auto-init-sra-1.c: New test.
	* gcc.dg/auto-init-sra-2.c: New test.
	* gcc.dg/auto-init-uninit-1.c: New test.
	* gcc.dg/auto-init-uninit-12.c: New test.
	* gcc.dg/auto-init-uninit-13.c: New test.
	* gcc.dg/auto-init-uninit-14.c: New test.
	* gcc.dg/auto-init-uninit-15.c: New test.
	* gcc.dg/auto-init-uninit-16.c: New test.
	* gcc.dg/auto-init-uninit-17.c: New test.
	* gcc.dg/auto-init-uninit-18.c: New test.
	* gcc.dg/auto-init-uninit-19.c: New test.
	* gcc.dg/auto-init-uninit-2.c: New test.
	* gcc.dg/auto-init-uninit-20.c: New test.
	* gcc.dg/auto-init-uninit-21.c: New test.
	* gcc.dg/auto-init-uninit-22.c: New test.
	* gcc.dg/auto-init-uninit-23.c: New test.
	* gcc.dg/auto-init-uninit-24.c: New test.
	* gcc.dg/auto-init-uninit-25.c: New test.
	* gcc.dg/auto-init-uninit-26.c: New test.
	* gcc.dg/auto-init-uninit-3.c: New test.
	* gcc.dg/auto-init-uninit-34.c: New test.
	* gcc.dg/auto-init-uninit-36.c: New test.
	* gcc.dg/auto-init-uninit-37.c: New test.
	* gcc.dg/auto-init-uninit-4.c: New test.
	* gcc.dg/auto-init-uninit-5.c: New test.
	* gcc.dg/auto-init-uninit-6.c: New test.
	* gcc.dg/auto-init-uninit-8.c: New test.
	* gcc.dg/auto-init-uninit-9.c: New test.
	* gcc.dg/auto-init-uninit-A.c: New test.
	* gcc.dg/auto-init-uninit-B.c: New test.
	* gcc.dg/auto-init-uninit-C.c: New test.
	* gcc.dg/auto-init-uninit-H.c: New test.
	* gcc.dg/auto-init-uninit-I.c: New test.
	* gcc.target/aarch64/auto-init-1.c: New test.
	* gcc.target/aarch64/auto-init-2.c: New test.
	* gcc.target/aarch64/auto-init-3.c: New test.
	* gcc.target/aarch64/auto-init-4.c: New test.
	* gcc.target/aarch64/auto-init-5.c: New test.
	* gcc.target/aarch64/auto-init-6.c: New test.
	* gcc.target/aarch64/auto-init-7.c: New test.
	* gcc.target/aarch64/auto-init-8.c: New test.
	* gcc.target/aarch64/auto-init-padding-1.c: New test.
	* gcc.target/aarch64/auto-init-padding-10.c: New test.
	* gcc.target/aarch64/auto-init-padding-11.c: New test.
	* gcc.target/aarch64/auto-init-padding-12.c: New test.
	* gcc.target/aarch64/auto-init-padding-2.c: New test.
	* gcc.target/aarch64/auto-init-padding-3.c: New test.
	* gcc.target/aarch64/auto-init-padding-4.c: New test.
	* gcc.target/aarch64/auto-init-padding-5.c: New test.
	* gcc.target/aarch64/auto-init-padding-6.c: New test.
	* gcc.target/aarch64/auto-init-padding-7.c: New test.
	* gcc.target/aarch64/auto-init-padding-8.c: New test.
	* gcc.target/aarch64/auto-init-padding-9.c: New test.
	* gcc.target/i386/auto-init-1.c: New test.
	* gcc.target/i386/auto-init-2.c: New test.
	* gcc.target/i386/auto-init-21.c: New test.
	* gcc.target/i386/auto-init-22.c: New test.
	* gcc.target/i386/auto-init-23.c: New test.
	* gcc.target/i386/auto-init-24.c: New test.
	* gcc.target/i386/auto-init-3.c: New test.
	* gcc.target/i386/auto-init-4.c: New test.
	* gcc.target/i386/auto-init-5.c: New test.
	* gcc.target/i386/auto-init-6.c: New test.
	* gcc.target/i386/auto-init-7.c: New test.
	* gcc.target/i386/auto-init-8.c: New test.
	* gcc.target/i386/auto-init-padding-1.c: New test.
	* gcc.target/i386/auto-init-padding-10.c: New test.
	* gcc.target/i386/auto-init-padding-11.c: New test.
	* gcc.target/i386/auto-init-padding-12.c: New test.
	* gcc.target/i386/auto-init-padding-2.c: New test.
	* gcc.target/i386/auto-init-padding-3.c: New test.
	* gcc.target/i386/auto-init-padding-4.c: New test.
	* gcc.target/i386/auto-init-padding-5.c: New test.
	* gcc.target/i386/auto-init-padding-6.c: New test.
	* gcc.target/i386/auto-init-padding-7.c: New test.
	* gcc.target/i386/auto-init-padding-8.c: New test.
	* gcc.target/i386/auto-init-padding-9.c: New test.

1 files changed, 34 insertions, 20 deletions

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index 3f2c176..dd0e6b5 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -4518,12 +4518,14 @@ clear_padding_add_padding (clear_padding_struct *buf,
     }
 }
 
-static void clear_padding_type (clear_padding_struct *, tree, HOST_WIDE_INT);
+static void clear_padding_type (clear_padding_struct *, tree,
+				HOST_WIDE_INT, bool);
 
 /* Clear padding bits of union type TYPE.  */
 
 static void
-clear_padding_union (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
+clear_padding_union (clear_padding_struct *buf, tree type,
+		     HOST_WIDE_INT sz, bool for_auto_init)
 {
   clear_padding_struct *union_buf;
   HOST_WIDE_INT start_off = 0, next_off = 0;
@@ -4568,7 +4570,7 @@ clear_padding_union (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
 	      continue;
 	    gcc_assert (TREE_CODE (TREE_TYPE (field)) == ARRAY_TYPE
 			&& !COMPLETE_TYPE_P (TREE_TYPE (field)));
-	    if (!buf->clear_in_mask)
+	    if (!buf->clear_in_mask && !for_auto_init)
 	      error_at (buf->loc, "flexible array member %qD does not have "
 				  "well defined padding bits for %qs",
 			field, "__builtin_clear_padding");
@@ -4579,7 +4581,7 @@ clear_padding_union (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
 	union_buf->off = start_off;
 	union_buf->size = start_size;
 	memset (union_buf->buf, ~0, start_size);
-	clear_padding_type (union_buf, TREE_TYPE (field), fldsz);
+	clear_padding_type (union_buf, TREE_TYPE (field), fldsz, for_auto_init);
 	clear_padding_add_padding (union_buf, sz - fldsz);
 	clear_padding_flush (union_buf, true);
       }
@@ -4649,7 +4651,8 @@ clear_padding_type_may_have_padding_p (tree type)
      __builtin_clear_padding (buf.base);  */
 
 static void
-clear_padding_emit_loop (clear_padding_struct *buf, tree type, tree end)
+clear_padding_emit_loop (clear_padding_struct *buf, tree type,
+			 tree end, bool for_auto_init)
 {
   tree l1 = create_artificial_label (buf->loc);
   tree l2 = create_artificial_label (buf->loc);
@@ -4660,7 +4663,7 @@ clear_padding_emit_loop (clear_padding_struct *buf, tree type, tree end)
   g = gimple_build_label (l1);
   gimple_set_location (g, buf->loc);
   gsi_insert_before (buf->gsi, g, GSI_SAME_STMT);
-  clear_padding_type (buf, type, buf->sz);
+  clear_padding_type (buf, type, buf->sz, for_auto_init);
   clear_padding_flush (buf, true);
   g = gimple_build_assign (buf->base, POINTER_PLUS_EXPR, buf->base,
 			   size_int (buf->sz));
@@ -4678,10 +4681,16 @@ clear_padding_emit_loop (clear_padding_struct *buf, tree type, tree end)
 }
 
 /* Clear padding bits for TYPE.  Called recursively from
-   gimple_fold_builtin_clear_padding.  */
+   gimple_fold_builtin_clear_padding.  If FOR_AUTO_INIT is true,
+   the __builtin_clear_padding is not called by the end user,
+   instead, it's inserted by the compiler to initialize the
+   paddings of automatic variable.  Therefore, we should not
+   emit the error messages for flexible array members to confuse
+   the end user.  */
 
 static void
-clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
+clear_padding_type (clear_padding_struct *buf, tree type,
+		    HOST_WIDE_INT sz, bool for_auto_init)
 {
   switch (TREE_CODE (type))
     {
@@ -4765,7 +4774,7 @@ clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
 		  continue;
 		gcc_assert (TREE_CODE (ftype) == ARRAY_TYPE
 			    && !COMPLETE_TYPE_P (ftype));
-		if (!buf->clear_in_mask)
+		if (!buf->clear_in_mask && !for_auto_init)
 		  error_at (buf->loc, "flexible array member %qD does not "
 				      "have well defined padding bits for %qs",
 			    field, "__builtin_clear_padding");
@@ -4781,7 +4790,8 @@ clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
 		gcc_assert (pos >= 0 && fldsz >= 0 && pos >= cur_pos);
 		clear_padding_add_padding (buf, pos - cur_pos);
 		cur_pos = pos;
-		clear_padding_type (buf, TREE_TYPE (field), fldsz);
+		clear_padding_type (buf, TREE_TYPE (field),
+				    fldsz, for_auto_init);
 		cur_pos += fldsz;
 	      }
 	  }
@@ -4821,7 +4831,7 @@ clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
 	  buf->align = TYPE_ALIGN (elttype);
 	  buf->off = 0;
 	  buf->size = 0;
-	  clear_padding_emit_loop (buf, elttype, end);
+	  clear_padding_emit_loop (buf, elttype, end, for_auto_init);
 	  buf->base = base;
 	  buf->sz = prev_sz;
 	  buf->align = prev_align;
@@ -4831,10 +4841,10 @@ clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
 	  break;
 	}
       for (HOST_WIDE_INT i = 0; i < nelts; i++)
-	clear_padding_type (buf, TREE_TYPE (type), fldsz);
+	clear_padding_type (buf, TREE_TYPE (type), fldsz, for_auto_init);
       break;
     case UNION_TYPE:
-      clear_padding_union (buf, type, sz);
+      clear_padding_union (buf, type, sz, for_auto_init);
       break;
     case REAL_TYPE:
       gcc_assert ((size_t) sz <= clear_padding_unit);
@@ -4858,14 +4868,14 @@ clear_padding_type (clear_padding_struct *buf, tree type, HOST_WIDE_INT sz)
       break;
     case COMPLEX_TYPE:
       fldsz = int_size_in_bytes (TREE_TYPE (type));
-      clear_padding_type (buf, TREE_TYPE (type), fldsz);
-      clear_padding_type (buf, TREE_TYPE (type), fldsz);
+      clear_padding_type (buf, TREE_TYPE (type), fldsz, for_auto_init);
+      clear_padding_type (buf, TREE_TYPE (type), fldsz, for_auto_init);
       break;
     case VECTOR_TYPE:
       nelts = TYPE_VECTOR_SUBPARTS (type).to_constant ();
       fldsz = int_size_in_bytes (TREE_TYPE (type));
       for (HOST_WIDE_INT i = 0; i < nelts; i++)
-	clear_padding_type (buf, TREE_TYPE (type), fldsz);
+	clear_padding_type (buf, TREE_TYPE (type), fldsz, for_auto_init);
       break;
     case NULLPTR_TYPE:
       gcc_assert ((size_t) sz <= clear_padding_unit);
@@ -4901,7 +4911,7 @@ clear_type_padding_in_mask (tree type, unsigned char *mask)
   buf.sz = int_size_in_bytes (type);
   buf.size = 0;
   buf.union_ptr = mask;
-  clear_padding_type (&buf, type, buf.sz);
+  clear_padding_type (&buf, type, buf.sz, false);
   clear_padding_flush (&buf, true);
 }
 
@@ -4911,9 +4921,13 @@ static bool
 gimple_fold_builtin_clear_padding (gimple_stmt_iterator *gsi)
 {
   gimple *stmt = gsi_stmt (*gsi);
-  gcc_assert (gimple_call_num_args (stmt) == 2);
+  gcc_assert (gimple_call_num_args (stmt) == 3);
   tree ptr = gimple_call_arg (stmt, 0);
   tree typearg = gimple_call_arg (stmt, 1);
+  /* the 3rd argument of __builtin_clear_padding is to distinguish whether
+     this call is made by the user or by the compiler for automatic variable
+     initialization.  */
+  bool for_auto_init = (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 2));
   tree type = TREE_TYPE (TREE_TYPE (typearg));
   location_t loc = gimple_location (stmt);
   clear_padding_struct buf;
@@ -4970,7 +4984,7 @@ gimple_fold_builtin_clear_padding (gimple_stmt_iterator *gsi)
 	  buf.sz = eltsz;
 	  buf.align = TYPE_ALIGN (elttype);
 	  buf.alias_type = build_pointer_type (elttype);
-	  clear_padding_emit_loop (&buf, elttype, end);
+	  clear_padding_emit_loop (&buf, elttype, end, for_auto_init);
 	}
     }
   else
@@ -4983,7 +4997,7 @@ gimple_fold_builtin_clear_padding (gimple_stmt_iterator *gsi)
 	  gsi_insert_before (gsi, g, GSI_SAME_STMT);
 	}
       buf.alias_type = build_pointer_type (type);
-      clear_padding_type (&buf, type, buf.sz);
+      clear_padding_type (&buf, type, buf.sz, for_auto_init);
       clear_padding_flush (&buf, true);
     }